Customary clutches in torque converters are actuated for engagement in order to connect the input drive to the output drive of the torque converter, wherein a direct drive shaft exists from the input drive to the output drive, resulting in improved efficiency. These clutches are frequently actuated for engagement when the turbine torque is the same as the pump torque when the clutch is engaged or disengaged. These shift points are determined by a rotational speed difference between the pump wheel and the turbine wheel of the hydrodynamic torque converter.
DE 35 17 381 C2 describes a lock-up control mechanism for the torque converter of an automatic transmission having a multi-stage transmission with which a lock-up clutch is provided for the hydrodynamic torque converter, wherein for each gear shifting the power-lock clutch is first re-engaged during upshifting when the rotational speed at the output of the torque converter has been decreased, while the lock-up clutch is disengaged by a predetermined rotational speed difference.